The present invention relates to optical systems, and more particularly concerns devices for folding an optical beam so as to increase its beam length.
Many devices for processing optical beams have significant size restrictions, yet require relatively long lengths for the beams inside the devices.
A common technique for increasing the length of a beam within an optical device is to fold the beam inside the device. Binoculars, for example, commonly reflect incident optical beams in a xe2x80x9cZxe2x80x9d shape to increase their optical length while keeping their physical length small. Many reflex cameras employ a pentaprism to increase the optical length of their viewfinders within a small camera body. Projection systems of various kinds attain wider deflection angles in a shorter distance from projector to screen by folding their beams internally. Projection television receivers, for example, frequently employ shaped mirrors to fold the beams traveling from the guns to the screen. Collimators and other types of devices can achieve increased beam length by folding incident optical beams within the devices. Heads-up displays and helmet-mounted military optics require multiple optical functions in a small volume. Other kinds of radiation beams, such as x-rays and electron beams, can also be processed by folding them in suitable devices.
A number of conventional devices fold optical beams with plane mirrors or other reflectors. Beam folders implemented with conventional reflectors generally do not save large amounts of space. That is, at least one physical dimension of such a device remains a large fraction of the effective optical length within the boundaries of the device. Other conventional folding devices employ beam splitters. These devices can significantly increase optical length compared to their physical dimensions. However, beam splitters typically suffer from low optical efficiency. The intensity of the output beam is frequently only a small fraction of the incident beam""s strength. In addition, such devices do not perform other optical functions within the device. Their only function is to increase path length; any further beam manipulation must be accomplished separately, thus increasing the overall volume of the device.
The present invention offers optical devices for increased optical length in restricted volumes using polarizing beam splitters reflectors that repolarize or convert the polarization of an incident beam, thus providing greater optical manipulation of the beam in a given physical space. Some of the devices employ polarized beams, others operate with non-polarized beams.
Devices according to the invention include one or more polarizing beam splitters each having a pass axis that transmits one polarization of an incident beam through the splitter, and a rejection axis that reflects a different polarization from the splitter in a different direction. Devices incorporating the invention also include one or more repolarizing reflectors, that is, reflectors that change both the direction of an incident beam and its polarization. These elements are configured to transmit an incident beam entering the device among each other so that one or more of the splitters both passes and rejects the beam because of a polarization change in one or more of the reflectors.
The invention finds utility in optical systems for many applications, such as projectors, imagers, collimators, and manipulators of optical and similar radiation. The terms xe2x80x9copticalxe2x80x9d and xe2x80x9clightxe2x80x9d must be taken in a broad sense as including any wavelength and type of radiated energy.